1. Field of the Invention
The present invention relates to an apparatus for heating a green tire during vulcanizing process or the preceding process thereof.
2. Description of the Related Art
Conventionally, a green tire formed by a forming machine is kept in a rack of keeping place set inside a building of a vulcanizing facilities and the like under room temperature conditions, and is taken from the rack to convey to a vulcanizing machine based on a production plan. If the green tire is carried in the vulcanizing machine, for example in a bladder type vulcanizing machine, the green tire is loaded into a mold by clamping the mold, and then a heat medium under high temperature and high pressure is supplied in a bladder inserted into a tire hole, so that the bladder is extended to be close to an inner wall surface of the tire. And, by heating the inner wall surface of the tire while pressurizing it in a mold direction via the bladder, a tire groove of the mole is formed in a tread portion of the green tire. Also, by heating the green tire from the inside and the outside using the heated mold and the bladder contacting to the heat medium of high temperature, to rise temperature of the green tire up to a vulcanizing initiation temperature (at least 100xcx9c120xc2x0 C.) early, it is possible to complete a vulcanizing process in a short time.
However, as above-described prior art, if the green tire is kept for a long time under room temperature conditions, then the green tire becomes the temperature near room temperature, for example 25xc2x0 C., therefore it is necessary to rise the temperature of the green tire from room temperature to initial temperature of vulcanizing when vulcanizing formation the green tire in the vulcanizing machine. In the prior art, as described above, although the vulcanizing process is completed in a short time by heating the green tire from the inside and the outside using the mold and the bladder, but the green tire has a rubber of which heat transfer ratio is low as a main component, therefore though temperature of a surface of the green tire is raised in a short time, the temperature rising of inner center particularly in a large thickness portion of the tread having large thickness and bead portion is remarkably delayed. Accordingly, vulcanizing process must be continued until temperature of the inside of the green tire is raised to complete the vulcanization, even when vulcanization of the surface side of the green tire is completed, therefore there is a problem that the vulcanizing process could not completed in a sufficiently short time.
Also, a method of irradiating a micro wave to a green tire when the green tire is kept, for preheating the green tire before vulcanizing process is adopted. But in this method, the macro wave preheats (heat) mainly the surface side of the green tire and the inside in which the temperature rising is most delayed upon vulcanization, can not be preheated sufficiently, therefore it is not a fundamental solution for completing vulcanizing process in a short time.
Furthermore, such problems are caused in a various type of a vulcanizing machine such a bladder type, a bladder-less type etc., and particularly in the bladder type vulcanizing machine, the problems become more serious since the bladder itself is formed of rubber having low heat conduction ratio.
Also, as disclosed in Japanese Patent Laid-Open No. Hei 7-96525, there is known a technique that a green tire comprising a bead and belt layer of conductive material is heated from the inside, by generating a magnetic field in the portion of the bead and belt layer to induce over-current due to electromagnetic induction thereby generating heat. However, the study has not been made for how to constitute an apparatus for efficiently heating when adopting the heating method to the vulcanization of green tire.
Therefore, the object of the present invention is to provide an apparatus for effectively heating a green tire using a heating method by means of electromagnetic induction, thereby completing a heating formation of a green tire in a sufficiently short time.
To solve the above problem, according to one aspect of the present invention, there is provided an apparatus for heating a green tire by generating heat to a metal member embedded in the green tire using electromagnetic induction, comprising: a local heating coil for forming high frequency magnetic field along a portion of an extending direction of said metal member; a high frequency power supply for supplying high frequency power to said local heating coil; and moving means for moving said local heating coil relatively in the extending direction of said metal member.
With above construction, since the local heating coil forms high frequency magnetic field along a portion of extending direction of said metal member, heat generation effect on the portion of the metal member is increased. At this time, it is possible to heat the whole metal member efficiently, by relatively moving the local heating coil and said metal member.
Here, said local heating coil can form high frequency magnetic field along a portion of facial direction of a ring-belt-shaped metal member embedded in a tread portion of said green tire, or can form high frequency magnetic field along a portion of peripheral direction of a wire-ring-shaped metal member embedded in a tread portion of said green tire.
Also, said local heating coil can comprise a center core, a side core and a coil, and at least one of said center core, said core and said coil can have a deformed portion, and said deformed portion may be formed so as to concentrate high frequency magnetic field to said tread portion or a shoulder portion continued from said tread portion.
In some cases, the shoulder portion is positioned at the both ends of the ring-belt-shaped metal member and curved in a width direction, or thickness of the shoulder portion is thicker than that of the tread portion. In such cases, heating to the shoulder portion becomes more necessary. According to the above construction, the deformed portion thereof concentrates magnetic flux on the both ends of a width direction of the ring-belt-shaped metal member positioned at the shoulder portion, so that it is possible to increase heat generation efficiency at these portions.
Said center core can be formed as a curved surface or stepped shape so as to follow the periphery of said green tire.
With above construction, since the center core is formed as a curved surface or stepped shape corresponding to R shape of peripheral direction of the green tire, the magnetic flux is easily formed along the peripheral direction of the ring-belt-shaped metal member and heat generation efficiency of the ring-belt-shaped metal member can be improved.
Said local heating coil can be installed apart in a width direction of said tread portion and can be constructed to have installation interval variable in response to the green tire size.
With above construction, the magnetic flux can be formed in the whole width direction, by adjusting the installation interval of said local heating coil in response to size of width direction of the ring-belt-shaped metal member.
Said local heating coil can be constructed to comprise a spiral coil and a core arranged on a side of said spiral coil.
With above construction, high frequency magnetic field is formed along peripheral direction of the wire-ring-shaped metal member, so that the wire-ring-shaped metal member is heated efficiently.
Said spiral coil can have an approximately elliptical shape following said wire-ring-shaped metal member and said core may have a square shape following said wire-ring-shaped metal member.
With above construction, the spiral coil having an approximately elliptical shape forms magnetic field efficiently following the wire-ring-shaped metal member.
Said moving means can be a rotational driving mechanism for rotating said green tire about a center axis thereof.
With above construction, it is possible to realize uniform heating of the whole metal member more efficiently.
Furthermore, said local heating coil can be placed between a pair of green tires so that it can heat said pair of green tire simultaneously.
Said local heating coil can be provided so as to heat one green tire, and a ferrite core can be disposed opposite to said green tire with respect to said local heating coil.
With above construction, magnetic flux opposite to the green tire is converged so that heating efficiency can be increased.
The apparatus can further comprise an auxiliary core, and said auxiliary core can be disposed so as to raise the density of high frequency magnetic field of said shoulder portion.
With above construction, magnetic flux is concentrated on both ends of width direction of the ring-belt-shaped metal member positioned at the shoulder portion, so that heating efficiency at this portion can be increased.
According to other aspect of the present invention, there is provided, an apparatus for heating a green tire by generating heat to a metal member embedded in the green tire using electromagnetic induction, comprising: a heating coil for forming high frequency magnetic field along a portion of an extending direction of said metal member, said heating coil being constructed to be insertable through a tire hole of said green tire; and a high frequency power supply for supplying high frequency power to said heating coil, wherein said heating coil is disposed so that both ends thereof are positioned in the vicinity of both bead portions of said green tire.
With above construction, high frequency magnetic field produced from a columnar heating coil inserted through the tire hole induction-heats a metal member of the tread portion and a metal member of the bead portion, so that it is possible to sufficiently perform preheating particularly, of the tire inside of tread portion and bead portion having large thickness where temperature rising is delayed. Additionally, since the metal member of the tread portion and bead portion can be induction-heated using only one columnar heating coil, it is possible to save the cost of components and cost for assembling.
According to another aspect of the present invention, there is provided, an apparatus for heating a green tire by generating heat to a metal member embedded in the green tire using electromagnetic induction, comprising: a heating coil for forming high frequency magnetic field along a portion of an extending direction of said metal member; a high frequency power supply for supplying high frequency power to said heating coil, and a magnetic material member for inducing high frequency magnetic field formed by said heating coil to said metal member.
With above construction, since high frequency magnetic field to be produced by the heating coil passes through the metal member and is formed to converge onto the magnetic material, magnetic flux density passing through the metal member becomes large and the metal member can be induction-heated efficiently.
According to another aspect of the present invention, there is provided, an apparatus for heating a green tire by generating heat to a metal member embedded in the green tire using electromagnetic induction, comprising: a heating coil for forming high frequency magnetic field along a portion of an extending direction of said metal member; a high frequency power supply for supplying high frequency power to said heating coil, and frequency changing means for changing the frequency of power to be supplied by said high frequency power supply.
The structure of the metal member embedded in the inside of tire is different according to type or size of the tire. With above construction, since the frequency can be changed suitably in response to wire diameter or current permeate depth thereof, it is possible to heat the metal member by induction efficiently.
Here, the apparatus can further comprise a condenser for causing a resonance current to said heating coil.
With above construction, since the resonance current is formed by means of the condenser, heat generation efficiency of the whole apparatus can be improved, and it is possible to improve the power-factor and to heat the metal member by induction efficiently.
Moreover, the apparatus can further comprises a voltage detector for detecting voltage applied to both ends of said condenser, and said frequency changing means may control the frequency of power to be supplied by said high frequency power supply on the basis of voltage value detected by said voltage detector.
According to another aspect of the present invention, there is provided, an apparatus for heating a green tire by generating heat to a metal member embedded in the green tire using electromagnetic induction, comprising: a heating coil for forming high frequency magnetic field along a portion of an extending direction of said metal member; a high frequency power supply for supplying high frequency power to said heating coil, and relative distance adjusting means which is capable of adjusting the distance between said heating coil and said metal member.
With above construction, since the magnetic flux density passing through the metal member can be adjusted in response to material constitution or shape of the metal member, it is possible to heat the metal member by induction efficiently.
It is preferred that the apparatus for heating a green tire according to the present invention is used as preheating apparatus for performing the preheating before the green tire enters into a green tire vulcanizing apparatus.
With this invention, a large thickness portion which is difficult to rise temperature is preliminarily temperature-raised to some degree, so that it is effective to complete a later vulcanizing process in a more short time.